Device for providing a continuous biological decomposition of minerals and concentrates thereof

ABSTRACT

A lying rotatable drum for continuous biological decomposition which includes at least one transversal partition for dividing the container interior into chambers. The partition has opening to transmit liquid between the chambers. Guide means are also provided.

The invention refers to a device for providing a continuous biologicaldecomposition of minerals and concentrates thereof by means of aerobicmicro-organisms and comprising a lying elongated rotatable containerwith inlets and outlets at the ends thereof for mineral and nutritionsolutions and bacteria and gas, internal guide means for circulation andoxygenization of the liquid mixture in the container and a drive devicefor rotating the container.

Biological d ition of mostly sulfide minerals has been used fro a longtime as a method for obtaining metals from ores. Various methods havebeen developed for utilizing various parts of the ore. As example itmight be mentioned that metal-poor wall rock from open pits is dumpedinto huge waste heaps, after which said heaps are sprayed with asolution containing a micro-organisms. From the leach solution obtainedat the bottom the metals then are recovered.

For a ground ore or a mineral concentrate from ore usually various typesof leach tanks are used. In said reacting tanks mineral concentrate,micro-organisms and nutrition solution are mixed and the metals then arerecovered from the leach solution obtained. Attempts also have been madeto connect several leach tanks with each other into a continuous system.In such case the mineral suspension has been pumped between the tanks ina constant flow or the flow between the tanks has been obtained byoverflow from one tank to another.

There are mainly two types of leach tanks which are present, namely theso-called "Pachucha" tank and a stirred reactor tank. In a continuoussystem both said types are fed with a pulp consisting of a slurry ofwater and mineral concentrate. The biological decomposition then occursin the tanks. The slurry is prepared in a separate storage tank. As faras the "Pachucha" tank is concerned, a strong air flow from below isused for addition of oxygen to the leach solution as well as forstirring so that the mineral particles do not settle. In the other typeof reactor tank there is a mechanical agitator and the addition ofoxygen usually occurs by introduction of air close to said agitator.

The capacity of both types of tanks is limited by the efficiency of thestirring. Particularly in continuous systems there is required ahomogeneous slurry in order to avoid settling and hence an accumulationof solid material in the tanks. In its turn, this limits the range ofparticle distribution and the pulp density. Too high pulp density alsomight have toxical effects on the organisms.

Therefore, further development of the continuous system has resulted ina new type of tank, a lying rotatable drum. In principle, such a drum isknown from U.S. Pat. No. 4,223,094 but the drum now suggested differsessentially from the known structure concerning feeding and dischargingas well as the internal design. Furthermore also the way of working andthe purpose differ essentially between the drums as well as the aerationof the solution.

The device according to the present invention is substantiallydistinguished by at least one transversal partition within the containerat a position between the ends thereof for dividing the containerinterior into chambers, said partition having a central opening fortransmission of the liquid mixture between the chambers, and in that theguide means are formed as profiles, mounted on and protruding radiallyinwardly from the inner wall of the container, which profiles in thechamber closest to the outlet end of the container extend parallel toeach other and to the longitudinal axis of the container, while profilesin the chamber adjacent to the inlet end of the container from anorientation parallel to the longitudinal axis of the container at thecontainer end are progressively curved towards the partition, and airsupply means furthermore being mounted in each of the chambers.

The inventive device is particularly well suited for treatment ofgoldbearing arsenopyrite/pyrite concentrates as well as for leachingprecious and rare earth metals and bulk concentrates of refractory ores.

By way of example, the invention will be further described below withreference to the accompanying drawing in which:

FIG. 1 is a diagrammatic perspective view in principle of a containeraccording to the invention,

FIG. 2 is a cross section through the container taken along the lineII--II in FIG. 1, and

FIG. 3 is a longitudinal section of the container.

As is illustrated in the drawing, the device according to the inventioncomprises a lying rotatable drum 1, adapted for continuous biologicaldecomposition of mineral concentrate by means of aerobicmicro-organisms. The drum 1 is tubular and closed at the ends by plates2a, 2b, which either are attached to the drum 1 or stationary, such thatthe drum 1 rotates relative said plates. The feeding and discharging ofmaterial and bacteria and the solutions incorporated in the slurry 10occurs through openings 3a, 3b in said end plates 2a, 2b (FIG. 1). Inthe first-mentioned case the openings 3a, 3b in the end plates 2a, 2bmust be centrally located. In the latter case when the end plates 2a, 2bthus are stationary when the drum rotates, the openings 3a, 3b do notneed to lie in the center but can be located as desired. The locationand size of the openings 3a, 3b is determining for the working volume inthe drum 1. Contrary to the disclosure of U.S. Pat. No. A 4,223,094 thedrum constitutes an entirely open system and the discharge occurs byoverflow.

By means of one or more partitions 4 secured to the drum 1, the same isdivided into at least two sections or chambers x, y. The transport ofmaterial between said sections occurs through a centrally locatedopening 5 in the partition 4. The size of the opening controls thequantity of material transported between the sections x, y of the drum(FIG. 1).

In the sections x, y control means or so-called baffles 6a, 6b aremounted along the walls of the container. In the first section x as seenin the direction of flow, the feeding side, which forms a mixingchamber, said baffles have helical shape with progressively increasedcurvature such that the settled material is returned towards the endwall 2a. Closest to said end wall 2a, however, the baffles 6a areparallel, so that added grinding bodies 7 will assist in providing amechanical decomposition (FIG. 1). Contrary to the "Pachucha" tank andthe stirred reactor tank the drum 1 has no difficulties in coping with acertain sedimentation and therefore a wide range of particle sizes doesnot imply any limitations. Furthermore the average pulp density might behigher than in the two aforementioned known tank types since a slowrotation of the drum (<15 rpm) with a high pulp density implies that aportion of the heavier fractions will settle which reduces the risk of atoxical effect on the organisms (FIG. 2). It is this portion 11 of thesolid material which then is treated by means of the added grindingbodies 7.

In the last section y at the discharge side, which is a reactionchamber, all baffles 6b are parallel over the entire length in order notto restrict the transport towards the discharge opening 3b, but at thesame time, they have to assist in the continued mechanical decompositionby means of grinding bodies 7. By a further partition 4, an intermediatesection z can be formed as seen in FIGS. 1 and 3, which also forms areaction chamber and has oppositely helically curved baffles 6a in orderto increase the mixing and to contribute to the mechanical decompositionby means of added grinding bodies.

The required supply of oxygen to the tank is made by pumping air intothe solution through the baffles or through tubes 8 submerged in thesolution and introduced through the openings 3a, 3b in the end plates2a, 2b (FIG. 3).

We claim:
 1. In a device for providing a continuous biologicaldecomposition of minerals and concentrates thereof by means of aerobicmicro-organisms and comprising a lying elongated rotatable container (1)with inlets and outlets (3a, 3b, respectively) at ends thereof formineral and nutrition solutions and bacteria and gas, internal guidemeans (6a, 6b) for circulation and oxygenization of a liquid mixture inthe container and a drive device for rotating the container, theimprovement comprising at least one transversal partition (4) within thecontainer (1) at a position between the ends thereof so as to divide thecontainer interior into at least two chambers, said partition (4) havinga central opening (5) for transmission of the liquid mixture between thechambers, and in that the guide means are formed as profiles (6a, 6b),mounted on and protruding radially inwardly from the inner wall of thecontainer, which profiles in the chamber (y) closest to the outlet endof the container extend parallel to each other and to the longitudinalaxis of the container, while the profiles in the chamber (x) adjacent tothe inlet end of the container from an orientation parallel to thelongitudinal axis of the container at the container inlet end areprogressively curved towards the partition, and air supply means (8)furthermore being mounted in each of the chambers (x, y, z).
 2. A deviceaccording to claim 1 wherein said at least one transversal partitioncomprises at least two transversal partitions forming at least oneintermediate chamber (z), wherein the guide profiles in saidintermediate chamber (z) have progressive helical curvature directedtowards said inlet end.